Chromium sulfate coated electrode



Jan, 16, 1951 E. K. SMITH I 2,538,054

CHROMIUM SULFATE COATED ELECTRODE Filed Sept. 10, 1949 FIG. 1.

' NON-EMISSIVE RADIATING comma E. K. s m??? Patented Jan. 16, 1951CHROMIUM SULFATE COATED ELECTRODE Earl K. Smith, West Orange, N. .L,assignor to Electrons, incorporated, Newark, N. .l., a corporation ofDelaware Application September 10, 1949, Serial No. 115,102

Claims.

This invention relates to electron discharge tubes, and moreparticularly to a surface film or coating for the electrodes of suchtubes to facilitate heat: radiation and reduce electron emission fromthe electrode surface at its operating temperature.

One problem in the design and construction of electron discharge tubes,more particularly tubes having the higher current ratings, is that theanode and the control electrode tend to assume a high temperature inoperation and emit electrons to a degree to interfere with the properperformance of the tube. For example, during operation of a gas tubewith the higher continuous current rating, the anode tends to assume ahigh temperature due to bombardment by the electrons of the dischargecurrent; and excessive electron emission from the anode at such elevatedtemperature tends to reduce the negative or inverse voltage which thetube may stand without an arc-back or discharge through the tube in thewrong direction. Similarly, the control element or grid in such a tubetends to assume a high temperature due to heat radiated from the anodeand from the heat shielded cathode, and excessive electron emission fromthe grid is likely to prevent the grid from performing its propercontrolling function.

Such objectionable electron emission from electrodes depends of courseupon the temperature the electrode assumes in operation of the tube, andalso the nature of its surface as an emitter of electrons at a hightemperature level. The heat accumulated by electrodes during operationof a tube is dissipated largely by radiation, assisted by conduction ofheat to the outside of the tube envelope through the supporting elementsfor the electrode; and from the standpoint of temperature rise it isdesirable that the electrode should have a surface of good heatradiating qualities. Also, in addition to facilitating radiation of heatfrom an electrode to reduce its operating temperature, it is desirablehat the surface of the electrode should be such as to provide a minimumof electron emission at such operating temperature.

With these and other considerations in mind, the primary object of thisinvention is to provide a surface coating for electrodes of electrondischarge tubes which will facilitate heat radiation and reduce electronemission at the relatively high temperature the electrode may assume, ascompared with the plain metallic surface of the electrode. Morespecifically, this invention involves the formation of a coating orlayer of a sulphate of chromium on the surface of the electrode toimprove its heat radiating ualities and largely inhibit electronemission.

This application is a continuation-impart of my prior applications Ser.No. 12,726, filed March 3, 1948, and Ser. No. 12,725, filed March 3,1948 which issued on June 27, 1950 as Patent No. 2,513,255.

This invention may be employed for various types and forms of electrodesfor electron discharge tubes, under conditions Where improved heatradiation and reduced electron emissivity are desirable; and typicalexamples of such electrodes are illustrated in the accompanying drawmgs.

In these drawings, Fig. 1 illustrates the tantalum electrode of the tubeof my prior application, Ser. No. 12,726, with which the coating of asulphate of chromium in accordance with this invention may be used toadvantage; and Fig. 2 illustrates the grid of the tube disclosed in myprior application, Ser. No. 12,725, with which this same coating may beused to advantage.

Referring to Fig. 1, the tantalum anode illustrated comprises a circularthin sheet of tantalum with a peripheral flange 21, and radial ribs orcorrugations 28 to give this tantalum sheet sufiicient stiffness orrigidity to prevent excessive warping when heated. A pair of brackets 29of iron or steel are spot welded to the central portion of this anode Aat a large number of closely spaced points in accordance with thedisclosure of my prior patent, No. 2,456,540, December 14, 1948; and asupporting rod 30 attached to these brackets 29 facilitates supportingand sealing the anode in the tube envelope in the desired manner.

Referrin to Fig. 2, the control grid G herein illustrated comprises abody portion of concentric rings attached at the proper spaced intervalsto a pair of cross members Bl. This grid is arranged to be supported atits center and held against sidewise displacement in a manner notmaterial to the present invention, and illustrated and described indetail in my prior application Ser. No. 12,725, filed March 3, 1948.

The electrode coating characteristic of this invention consistsessentially of a sulphate of chromium closely bonded to the surface ofthe electrode, such as the tantalum anode at Fig. 1, or the grid of Fig.2 made of nickel or other material suitable for convenient fabricationof the parts.

This coating is preferably applied in accordance with the procedure orprocess described in my prior applications, Ser. No. 12,725 and Ser. No.12,726 above mentioned, and disclosed and claimed in my copendingapplication Ser. No. 115,103, filed September 10, 1949. It is found thatthe coating or film of a sulphate of chromium has a coefiicient of heatradiation much higher than the plain metal to which it is applied, andalso has the desired low degree electron emissivity at a relatively hightemperature.

It should be understood that the particular electrodes illustrated anddescribed merely represent typical applications of the heat radiatingand electron emission inhibiting coating characteristic of thisinventon, and that this coating may be applied to the various otherforms and types of electrodes.

What I claim is:

1. A tantalum anode for electron discharge tubes having a surfacecoating of a sulphate of chromium to increase its heat radiation andreduce its electron emission.

2. A tantalum anode for electron discharge tubes having baked thereon acoating of chromium sulphate for decreasing electron emission.

3. An electrode for electron discharge tubes comprising, a body of metalcapable of emitting electrons at an elevated temperature, and a coatingclosely bonded to the surface of said metal and consisting essentiallyof a sulphate of chromium.

4. A control grid for gas tubes comprising, a plurality of spaced gridbars having a uniform coating of a sulphate of chromium to reduceelectron emission from the grid for the same operating temperature.

5. An electrode for electron discharge tubes tending to assume arelatively high temperature in the operation of a tube, an electrodecomprising a body of a metal capable of emitting electrons at anelevated temperature, and a coating closely bonded to the surface ofsaid metal and consisting essentially of a sulphate of chromium forfacilitating radiation of heat from the electrode and reducing electronemission at said relatively high temperature.

EARL K. SMITH.

No references cited.

1. A TANTALUM ANODE FOR ELECTRON DISCHARGE TUBES HAVING A SURFACECOATING OF A SULPHATE OF CHROMIUM TO INCREASE ITS HEAT RADIATION ANDREDUCE ITS ELECTRON EMISSION.